Patent Document 1 discloses a spindle head including a fork-shaped driving portion (A-axis driving portion) that supports a spindle unit for rotating a spindle, to which a tool is attached, and that turns the spindle unit in a machine tool such as a so-called machining center.
The spindle unit rotates the spindle, which is rotatably supported in a housing of the spindle unit, by an internal spindle motor (also referred to as a built-in motor). A power line for supplying driving current is connected to the spindle motor, and this power line is led out from the housing of the spindle unit and is laid towards a power supply circuit in the machine tool.
In general, the power line is laid through the housing of the support head for supporting the spindle unit so as not to obstruct the turn of the spindle unit. For wiring from the spindle unit to the support head, the power line is sometimes led outside from a rear end portion (rear end face) of the spindle unit and is then led into the support head again. Sometimes a through hole is formed in a support shaft provided in the support head so as to support the spindle unit, and the power line is laid through the support shaft in a manner such as not to be exposed outside. In the conventional typical spindle head, when the power line is laid through the support shaft, as described above, only one of the support shafts on both sides of the spindle unit is capable of routing, and the power line extends from only one side of the spindle unit.
When the output of the spindle motor is increased to enhance productivity, the power line is thickened correspondingly. Further, when the spindle motor is of a coil switching type including a coil for high-speed rotation and a coil for low-speed rotation in order to drive the spindle at two speeds, that is, a low speed and a high speed, the number of power lines is doubled (for example, three power lines corresponding to U, B, and W phases of a three phase motor are doubled to six power lines).
In the routing path in the support shaft, not only the power line for the spindle motor, but also a signal line from a sensor (temperature sensor, rotation sensor for the motor) provided in the spindle unit is sometimes laid. Further, a pipe for supplying working fluid to the spindle unit is sometimes provided. Examples of this working fluid are air to be injected from near an end of the spindle towards the workpiece in order to prevent cutting chips produced during cutting from entering the spindle unit, cooling fluid for cooling the spindle motor, and coolant liquid for working.
In this way, not only a plurality of cables, such as power lines and signal lines, but also pipes for fluid supply are sometimes laid in the support shaft. When a plurality of cables and pipes are passed through the support shaft, there is no spatial room in the through hole of the support shaft, and a break may be caused by twisting and rubbing of the cables with the rotation of the support shaft. Further, since there is no spatial room, it may be impossible to pass a thicker power line and to be compatible with a high-output spindle motor. In the case of the power line, the bulk ratio of the space where the power line is passed is specified in design, and the power line cannot be passed through the space having little room.
Patent Document 1: U.S. Pat. No. 5,584,621